This invention relates generally to a stage system in which high precision positioning performance is required. The invention relates also to an exposure apparatus having such stage system for carrying a reticle or a wafer thereon for exposure of the same, and to a device manufacturing method using such exposure apparatus. In another aspect, the invention relates to a stage driving method effective to perform high precision positioning.
FIGS. 15A and 15B are schematic views of an example of known type stage system. A guide 802 is fixed to a base (not shown), and a stage 801 for carrying a workpiece 800 thereon is supported by the guide 802 slidably along one axial direction relative to it. There are linear motor moving elements 804 fixed at the opposite sides of the stage 801. Each moving element 804 faces to a linear motor stator 805 without contact thereto. The linear motor stators 805 are fixed to the base, not shown. Each linear motor moving element 804 comprises upper and lower integral structures of four-pole magnets 804a and yokes 804b for circulation of magnetic fluxes of the magnets. Each linear motor stator 805 comprises a plurality of coils 805a (six in this example) disposed in an array and being fixed together by a stator frame 805b. 
The linear motor 803 described above is an extended type of ordinary brushless DC motor, wherein the driving coil and the direction of electric current thereto are changed in accordance with the relative positional relationship between the magnet 804a and the coil 805a, whereby a desired force is produced in a desired direction.
In the structure described above, first, while the stage 801 is held stationary, an electric current is applied to predetermined linear motor coils in a predetermined direction and for a predetermined time period in accordance with the position of the stage 801 or of the magnets 804a, to produce acceleration of the stage 801. When a desired speed is reached, acceleration is finished and, while constant speed control is kept, a predetermined operation such as exposure or inspection, for example, is performed. After the constant speed period, an electric current is applied to predetermined linear motor coils in a predetermined direction and for a predetermined time period, to cause deceleration of the stage and to stop the stage motion.
The position of the stage is measured by using high precision position sensor means (not shown) such as a laser interferometer, for example, and an electric current is applied to linear motor coils separately from acceleration or deceleration, so as to avoid an error with respect to a target position. Thus, even during acceleration period, deceleration period and constant speed period, high precision position control is performed.
FIG. 16 is a schematic view of another example of known type stage system. This stage system is similar to one disclosed in Japanese Laid-Open Patent Application, Laid-Open No. 183192/1995. A guide 909 is mounted on a base 903, and a stage 907 is supported slidably relative to the guide 909. The base 903 is provided with an actuator unit 901 which serves to perform the positioning through expansion and contraction of its rod 905. Disposed between an end of the rod 905 and the stage 907 are a voice coil motor 906 and a clutch 904. The motor 906 comprises a coil-and-magnet structure (not shown), and a Lorentz force is produced in response to application of electric current to the coil, whereby a driving force is produced between the rod 905 and the stage 907.
In the structure described above, for driving the stage, first the clutch 904 is engaged through mechanical contact so that the rod 905 and the stage are held in connection. The driving force of the actuator unit 901 is thus transmitted to the stage, whereby rough motion of the stage is produced. The clutch 904 is disengaged after the stage rough motion, and the stage 907 is driven thereafter relative to the rod 905 with the driving force of the voice coil motor 906, to accomplish the positioning of the stage 907.
Since there is clutch 904 in parallel to voice coil motor 906, it does not need operation of the motor 906 for long-stroke stage driving with the actuator unit 901. Heat generation of the motor 906 is thus reduced.
When a stage is moved by using a linear motor only as in the first example described above, high precision positioning control is accomplished constantly. However, there is large heat generation in stage acceleration and deceleration. Also, the heat source is close to the workpiece. Further, since in a multi-phase linear motor such as described above the electric current is applied while changing the coils, it is difficult to cool the linear motor stator as a whole. For these reasons, some components adjacent to the workpiece may be deformed by thermal expansion or the measurement reference may be deformed by thermal expansion. Also, the air density along the light path of the laser interferometer may be disturbed. They may cause degradation of workpiece positioning precision. Additionally, thrust ripple to be produced when coils are changed may interfere precise positioning of the stage.
In a case of stage system wherein a voice coil motor and a clutch are provided in parallel between an actuator unit and a stage, as in the second example described above, since the clutch is held in engagement during the stage motion through the actuator unit, the voice coil motor is inoperative. In the rough motion period of the actuator unit, therefore, deviations to the stage target position may be accumulated, which means prolongation of positioning time required for the voice coil motor. Further, since the clutch is based on mechanical contact such as friction, there is a limit to stage precise positioning.
If the voice coil motor is operated while disengaging the clutch, in actuation of the actuator unit, the voice coil motor has to produce a large thrust force which causes large heat generation and lowered stage positioning precision.
Additionally, if the driving stroke of the voice coil motor is short, the stator of the motor must be positioned very precisely with respect to the moving element provided on the stage. In that case, the positioning of the rod by the actuator unit has to be performed vary precisely. However, the rod positioning control through the actuator unit is based on the current position of the stage as measured by the laser interferometer, it is very difficult to accomplish high precision positioning for the rod.
It is an object of the present invention to provide a high precision and high speed stage system by which at least one of the problems described above can be solved.
In accordance with an aspect of the present invention, there is provided a stage system, comprising: a stage being movable in a predetermined direction; a first unit for applying a force to the stage in the predetermined direction; moving means for moving one of the first unit and a structure including the first unit; first measuring means for measuring at least one of the position and movement amount of the stage; and second measuring means for measuring at least one of the position and movement amount of one of the first unit and the structure; wherein the stage is controlled on the basis of a measured value of said first measuring means, and wherein said moving means is controlled on the basis of a measured value of said second measuring means.
In preferred forms of this aspect of the present invention, the first unit may be controlled on the basis of a measured value of said first measuring means. The first unit may be controlled on the basis of information related to a target position of the stage. The first unit may include a linear motor. The first unit may have a function applying a force to a gravity center of the stage. The moving means may be controlled on the basis of information related to a target position of the stage. The moving means may include one of a linear motor and a ball screw. The stage may be made movable in three freedom directions. The first unit may be operable to apply a force to the stage in three freedom directions. The moving means may be operable to move one of the first unit and the structure in one freedom direction. The stage may be made movable in six freedom directions. The first unit may be operable to apply a force to the stage in six freedom directions. The moving means may comprise an X-Y stage. The stage system may further comprise a second unit separate from the first unit. The second unit may be controlled on the basis of information related to a target position of the stage. The second unit may be feed-forward controlled on the basis of information related to a target position of the stage. The information may concern acceleration of the stage. The second unit may have a function for applying a force to a gravity center of the stage.
The stage system may further comprise second moving means for moving one of the second unit and a second structure including the second unit. The moving means may be operable to move the first and second units integrally. The second unit may include an electromagnet. The second unit may include at least one set of electromagnets for producing forces opposite to each other and parallel to said predetermined direction. The second may be operable to apply a force to the stage in one freedom direction. The second unit may be operable to apply a force to the stage in two freedom directions.
In accordance with another aspect of the present invention, there is provided a stage system, comprising: a stage being movable in a predetermined direction; a first unit for applying a force to the stage in a predetermined direction; a second unit separate from the first unit, for applying a force to the stage in the predetermined direction; and moving means for moving one of the second unit and a structure including the second unit; wherein positioning of the stage is performed on the basis of the first unit, and wherein acceleration and deceleration of the stage are performed on the basis of the second unit.
In preferred forms of this aspect of the invention, the second unit may be operable to produce a force larger than that produced by the first unit. For production of the same driving force, heat generation of the second unit may be smaller than that of the first unit. The first unit may be operable to produce an electromagnetic force by use of a coil and a magnet, and the second unit may be operable to produce an attraction force by use of a magnetic element and an electromagnet. The second unit may include at least one set of electromagnets for producing forces opposite to each other and parallel to said predetermined direction. The stage system may further comprise first measuring means for measuring a position of the stage. The first unit may be controlled on the basis of a measured value of said first measuring means. The stage system may further comprise second measuring means for measuring at least one of a position and movement amount of the second unit. The moving means may be controlled on the basis of a measured value of said second measuring means.
The second unit may have a function of applying a force to the stage throughout a movement stroke of the stage. The moving means may be operable to move the first and second units integrally. The stage system may further comprise second moving means for moving one of the first unit and a second structure including the first unit. The stage system may further comprise third measuring means for measuring at least one of a position and movement amount of one of the first unit and the second structure including the first unit. The second moving means may be controlled on the basis of a measured value of said third measuring means. The stage system may further comprise acceleration information producing means for producing a signal related to acceleration of the stage, and positional information producing means for producing a signal related to a position of the stage, wherein the first unit may be controlled on the basis of a signal from said positional information producing means, and the second unit may be controlled on the basis of a signal from said acceleration information producing means.
The second unit may be feed-forward controlled on the basis of a signal from said acceleration information producing means. The moving means may be controlled on the basis of a signal from said positional information producing means. The stage may be made movable in three freedom directions. The first unit may be operable to apply a force to the stage in three freedom directions. The second unit may be operable to apply a force to the stage in one freedom direction. The moving means may be operable to move one of the first unit and the structure including the first unit, in one freedom direction. The stage may be made movable in six freedom directions. The first unit may be operable to apply a force to the stage in six freedom directions. The second unit may be operable to apply a force to the stage in two freedom directions. The moving means may have a function of moving one of the second unit and the structure including the second unit, in two freedom directions. The moving means may comprise an X-Y stage. The first unit may have a function of applying a force to a gravity center of the stage. The second unit may have a function of applying a force to a gravity center of the stage.
In accordance with a further aspect of the present invention, there is provided a stage system, comprising: a stage being movable in a predetermined direction; a unit for applying a force to the stage in the predetermined direction; moving means for moving one of the unit and a structure including the unit; first measuring means for measuring at least one of the position and movement amount of the stage; second measuring means for measuring at least one of the position and movement amount of one of the unit and the structure; and signal producing means for producing a signal on the basis of a target position of the stage; wherein the unit is controlled on the basis of a signal from said signal producing means and of a signal from said first measuring means, and wherein said moving means is controlled on the basis of a signal from said signal producing means and of a signal from said second measuring means.
In preferred forms of this aspect of the invention, the unit may be controlled on the basis of a difference between the signal from said signal producing means and a signal from said first measuring means. The moving means may be controlled on the basis of a difference between a signal from said signal producing means and a signal from said second measuring means. The signal from said signal producing means may relate to the position of the stage. The unit may include a linear motor. The stage system may further comprise a second unit separate from the unit, for applying a force to the stage. The second unit may be feed-forward controlled on the basis of a signal from said signal producing means. The second unit can be moved by one of said moving means and second moving means separate from said moving means. The second unit may include an electromagnet.
In accordance with a yet further aspect of the present invention, there is provided a stage system, comprising: a stage being movable in a predetermined direction; and a unit having a magnetic element and at least one set of electromagnets disposed on the opposite sides of the magnetic element; wherein one of the magnetic element and the electromagnets of the unit is held by the stage, and wherein the magnetic element and the electromagnets are kept opposed to each other regardless of rotational motion of the stage.
In preferred forms of this aspect of the invention, the magnetic element and the electromagnets may have opposed faces having one of a cylindrical shape and a spherical shape. The magnetic element may have one of an arcuate shape and a cup-like shape. The electromagnets may have an E-shape. An end face of the E-shape electromagnets may have one of an arcuate shape and a cup-like shape. The stage may be made movable in X and Y directions, and the unit may include at least two sets of electromagnets disposed to sandwich the magnetic element with respect to X and Y directions. The stage system may further comprise moving means for moving the other of the magnetic element and the electromagnets, not held by the stage, such that the magnetic element and the electromagnets can be held opposed to each other regardless of motion of the stage. The magnetic element may be disposed on the stage side. The stage system may further comprise adjusting means for adjusting a combined force of the electromagnets to a predetermined level. The unit may have a function of applying a force to a gravity center of the stage.
There may be provided an exposure apparatus and a device manufacturing method, using any one of the stage systems described above, within the scope of the present invention.
In accordance with a still further aspect of the present invention, there is provided a stage driving method, comprising: a first measuring step for measuring at least one of a position and movement amount of a stage being movable in a predetermined direction; a second measuring step for measuring at least one of a position and movement amount of one of a unit having an actuator and a structure including the unit; an applying step for applying a force to the stage through the unit; a moving step for moving the unit in a predetermined direction through moving means; a first control step for controlling the stage on the basis of a first measured value produced in said first measuring step; and a second control step for controlling at least one of the position and movement amount of one of the unit and the structure, on the basis of a second measured value produced in said second measuring step.
In preferred forms of this aspect of the invention, said second control step may include a step for controlling the unit. In the unit controlling step, the unit may be controlled on the basis of the first measured value and a target value. The method may further comprise a second applying step for applying a force to the stage through a second unit separate from the unit. The second unit may be feed-forward controlled on the basis of a target value.
In accordance with a still further aspect of the present invention, there is provided a stage driving method, comprising: a first measuring step for measuring at least one of a position and movement amount of a stage being movable in a predetermined direction; a second measuring step for measuring at least one of a position and movement amount of one of a unit having an actuator and a structure including the unit; an applying step for applying a force to the stage through the unit; a moving step for moving the unit in a predetermined direction through moving means; a signal producing step for producing a signal on the basis of a target position of the stage; a first control step for controlling the stage on the basis of a first measured value produced in said first measuring step and of a signal produced in said signal producing step; and a second control step for controlling at least one of the position and movement amount of one of the unit and the structure, on the basis of a second measured value produced in said second measuring step and a signal produced in said signal producing step. The method may further comprise detecting a difference between a signal produced in said signal producing step and the first measured value, or detecting a difference between a signal produced in said signal producing step and the second measured value.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.